Occipitocervical plate

ABSTRACT

Methods and systems for occipital-cervical spinal fixation. A plate configured for attachment to the occipital bone has two arms extending out from either side, which turn downwards parallel to one another. A first bend is disposed in the arms, such that the arms extend down from the occipital bone behind the spinous process of the C1 and C2 vertebrae, upon installation. A second bend in the arms allows attachment to the C2 vertebra. The system may be dimensioned for pediatric installation. A bone graft material may be held in place between the cervical vertebrae and the skull by installing a cable to the installed system to retain the bone graft material in place. Methods and kits for occipital-cervical spinal fixation are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority as a continuation-in-part of U.S.patent application Ser. No. 11/137,036, filed May 25, 2005, andpublished Jan. 5, 2006 as U.S. Patent Application Publication No. U.S.2006/0004363 A1, which itself, pursuant to the provisions of 35 U.S.C.§19(e), claims the benefit of the filing date of U.S. Provisional PatentApplication Ser. No. 60/574,282, filed May 25, 2004, for“OCCIPITOCERVICAL PLATE,” the contents of the entirety of each of whichare incorporated herein by this reference.

FIELD OF THE INVENTION

The present invention relates generally to apparatus and methods forspinal fixation. More specifically, the present invention relates toapparatus and methods for providing internal support and spinal fixationfor patients suffering from occipital-cervical instability.

BACKGROUND

Spinal fixation is a well known and frequently used medical procedure.Pedicle, lateral, and oblique mounting devices may be used to securecorrective spinal instrumentation to a portion of the spine that hasbeen selected to be fused by arthrodesis. Fixation of the skull to thecervical spine may be used to treat trauma to the neck, degenerativediseases such as rheumatoid arthritis, and congenital instability. Manycurrent implantable devices designed to immobilize the skull withrespect to the upper cervical spine are assemblies of several componentswhich are not designed specifically for fusing the cervical spine to theskull, but instead are assembled from multiple components designed forother applications. Such assembly may prolong and complicate theimplantation procedure.

A typical spinal fixation system includes corrective spinalinstrumentation that is attached to selected vertebrae of the spine byscrews, hooks, and clamps. Various types of screws, hooks, and clampshave been used for attaching such corrective spinal instrumentation toselected portions of a patient's spine. Examples of pedicle screws andother types of attachments are illustrated in U.S. Pat. Nos. 4,763,644;4,805,602; 4,887,596; 4,950,269; and 5,129,388. Each of these patents isincorporated by reference as if fully set forth herein. Examples of suchmultipart spinal fixation systems include U.S. Pat. Nos. 5,360,429 and5,542,946, the disclosure of each of which is incorporated by reference.

With respect to occipital-to-cervical spinal fixation systems, contouredloop and wire constructs, rod constructs, rod and plate constructs andpre-contoured “U-loop”-type constructs have been used. An example ofsuch a device is the OMI “U loop” device manufactured by Ohio MedicalInstruments. However, such devices have a number of limitations,including the lack of appropriately sized loops for children under fiveyears of age; the extensive modification and bending of the loopsrequired during surgery, which can lead to failure of the device evenbefore installation; cumbersome methods of coupling the devices to theanchor screws; and the lack of an option for installing a posteriorcervical screw, which can be an urgent need for patients with missinglamina or inadequate laminar bone quality.

With these multi-piece systems, a number of problems may occur. Forexample, pressure necrosis may occur at the points of hook or wirefixation, leading to failure. Supplementation of such systems with halovests often then fails to prevent micro-motion leading to non-union ofthe arthrodesis. Additionally, the time for surgery may be extended bythe need to build and install a multi-piece assembly from separatecomponents.

A few occipital-cervical spinal fixation systems, such as that disclosedin U.S. Pat. No. 6,146,382, the disclosure of which is incorporated byreference herein, attempt to simplify the implantation of the system byreducing the number of parts. A single plate attaches to an attachmentsite on the skull, and arms extend down from the plate to the cervicalvertebrae. The arms are coplanar with the plate and bend at the tipswhere a separate connection member is attached. The separate attachmentmember is then attached at the top surface of the C2 vertebra. A cableis then attached by a hook system to the plate to a vertebra posteriorto the arms, in order to retain a bone graft material in place. The '382device thus still includes a number of parts that are assembled in situ,retaining the issues described with multi-piece systems.

Approximately 500 surgical cases of pediatric occipito-cervical fusionsare performed in North America each year on children suffering fromoccipital-cervical instability. Current occipital-cervical fixationdevices, such as the '382 device, are designed for adults and aretherefore typically too large for use in children. Additionally, as therelationship of a child's head to the body differs from that of an adultdue to allometric growth, devices designed for adults may not sustainthe correct relationship of the head and neck for children. Surgicalconcerns are magnified when treating children, due to their smallerphysical size, the abnormal anatomy that may be caused bycraniovertebral anomalies, and their growth potential.

Previously, graft/wire constructs were reported to be associated with anonunion rate as high as 30% for C1-C2 fusion; however, this incidenceimproves considerably with the use of a halo orthosis. Transarticularscrew placement creates immediate atlantoaxial joint stability and, incontrast to previous posterior wiring/graft constructs, does not requirepostsurgical brace therapy. However, such procedures require surgicalprecision because serious potential risks are associated with improperscrew placement. Thus, many spine surgeons are reluctant to perform sucha procedure.

Accordingly, an occipital-cervical spinal fixation system that operatedas a single plate, not requiring the use of additional component plates,hooks or rods would be an improvement in the art. Such a system that isconfigured for use in children or small adults would be an additionalimprovement in the art.

SUMMARY OF THE INVENTION

One aspect of the present invention relates to occipital-cervical spinalfixation systems. In some embodiments the system includes a plateconfigured for attachment to the occipital bone, with two arms thatextend out from either side of the plate, with the distal end of thearms turning downwards parallel to one another. A bend is placed in thearms, such that the arms extend down from the occipital bone uponinstallation, behind the spinous process of the C1 and C2 vertebrae. Asecond bend is placed in the arms, allowing attachment to the C2vertebrae. Some embodiments are configured in appropriate dimensions forinstallation in a child for pediatric applications.

Other aspects of the present invention include methods of spinalfixation of the C1 and C2 vertebrae to the occiput. A one-piece spinalfixation system is attached to the C2 vertebra with a means forattaching the one-piece spinal fixation system to the C2 vertebra. Themeans for attaching the one-piece spinal fixation system to the C2vertebra may extend through the C2 vertebra into the C1 vertebra. Thesystem extends from the occipital bone, behind the spinous process ofthe C1 and C2 vertebrae. The means for attaching the one-piece spinalfixation system to the C2 vertebra may be transarticular screws such asheadless screws requiring only a single emplacement. The system isattached to the occipital bone by one or more means of attaching thesystem to the occipital bone. The means of attaching the system to theoccipital bone may be screws extending through a top plate. A bone graftmaterial may be held in place between the cervical vertebrae and theskull by installing a cable to the installed system to retain the bonegraft material in place.

BRIEF DESCRIPTION OF THE DRAWINGS

While the specification concludes with claims particularly pointing outand distinctly claiming that which is regarded as the present invention,the advantages of this invention and the best mode can be more readilyascertained from the following detailed description when read inconjunction with the accompanying drawings in which:

FIG. 1 is a side perspective view of an occipital-cervical fixationsystem, in accordance with the present invention.

FIG. 2 is a back view of the embodiment of FIG. 1.

FIG. 3 is a side view of the embodiment of FIGS. 1 and 2.

FIG. 4A is an exploded perspective view of screw and a retaining nut,useful with the system of FIGS. 1 to 3.

FIG. 4B is a perspective view of the retaining nut of FIG. 4A.

FIG. 4C is a top view of the screw of FIG. 4A.

FIG. 5 is a back view of emplacement of the screw of FIG. 4A in apatient, in accordance with the present invention.

FIGS. 6 and 7 are back views of the embodiment of FIGS. 1 to 3, shown insitu in a patient.

FIG. 8 is a side view of the embodiment of FIGS. 1 to 3, shown in situin a patient.

FIG. 9 is a backview of the embodiment of FIGS. 1 to 3, shown in situ ina patient, in conjunction with a bone graft material.

FIG. 10 is a back view of a second embodiment of an occipital-cervicalfixation system, in accordance with the present invention.

FIGS. 11A and 11B are back views of alternate embodiments of lowerattachment holes for embodiments of occipital-cervical fixation systemsin accordance with the present invention.

FIG. 12 is a side view of a screw and retaining nut attached to thesystem of FIGS. 1 to 3.

FIG. 13, is a horizontal cross-section of the screw and retaining nutdepicted in FIG. 12.

FIGS. 14A, 14B, and 14C, are various views of one example of a retainingnut according to the present invention. FIG. 14A being a vertical crosssection of the retaining nut; FIG. 14B being an end-on view of the upperend of the retaining nut; and FIG. 14C being an end-on view of the lowerend of the retaining nut.

DETAILED DESCRIPTION

FIGS. 1, 2 and 3 depict an illustrative embodiment of anoccipital-cervical spinal fixation system 10. An attachment plate 12 maybe configured for attachment to the occipital bone. Attachment plate 12may include an enlarged area 13, with one or more attachment holes 16,through which means of attaching the system to the occipital bone, forexample, attachment screws 42 (FIG. 6), may be placed to attach theplate to the occipital bone. Each of attachment holes 16 may includebeveled edges, allowing a means of attaching the system to the occipitalbone placed therein to lie flush with the plate surface (by beingcountersunk therein). As depicted, the plate 12 may be planar inconformation. The plate 12 may be contoured as desired to fit thesurface of the occiput prior to installation.

At opposite sides of plate 12, two arms 14A and 14B extend out from theplate 12 in opposite directions. Each arm 14 then extends downwardsbecoming generally parallel to one another and generally sharing acommon plane throughout their length. It will be appreciated that whilethe arms 14 may be generally parallels, some variation for individualpatients may be required, based on the patients anatomy. Viewed from thefront or back (as in FIG. 2), the relationship of the plate 12 and arms14A and 14B may generally resemble a horseshoe.

Each arm 14A or 14B contains a bend 20A or 20B in the length thereof, ata distance from the plate. The bends 20A and 20B are generally parallelto one another in the respective arms 14A and 14B, such that the arms14A and 14B remain generally parallel. Again, it will be appreciatedthat while the bends 20 and arms 14 may be generally parallels, somevariation for individual patients may be required, based on the patientsanatomy. The angle A of bends 20A and 20B is selected to ensure that,upon installation, the arms 14A and 14B extend down from the occipitalbone, behind the spinous process of the C1 and C2 vertebrae (as bestdepicted in FIG. 8). In one embodiment, an angle of about 115 to about135 degrees, as depicted in FIG. 3 as about 127 degrees, may be used. Itwill be appreciated that other angles may be used based upon the anatomyof the individual patient.

A second bend 30A and 30B may be placed in each arm, 14A and 14B,respectively, at a point distal to the first bend 20A or 20B. The secondbend 30A or 30B positions the distal end, such that it may be attachedto the lower surface of the spinous process of the C2 vertebrae (as bestdepicted in FIG. 8). In one embodiment, the angle B of bend 30A or 30Bmay be from about 140 to about 160 degrees, and as depicted in FIG. 2 asabout 151 degrees, although it will be appreciated that other angles maybe used, based upon the anatomy of the patient. Attachment may beaccomplished by insertion of at least one means of attaching theoccipital-cervical fixation to the C2 vertebra, such as, for example, aheadless screw 20 (FIG. 6), through a fastener hole 18A or 18B locatednear the distal end of the arm 14. Fastener hole 18A or 18B may includebeveled edges, allowing a means of attaching the occipital-cervicalfixation to the C2 vertebra placed therein to lie flush with the platesurface (by being countersunk therein). Longer means of attaching theoccipital-cervical fixation to the C2 vertebra such as, for example,headless screws 40, that extend through both the C1 and C2 vertebrae maybe used, where desirable for the procedure.

As will be appreciate by one of ordinary skill in the art, a means ofattaching the occipital-cervical fixation to the C2 vertebra may includea screw or any other device useful for attaching a vertebra to anexternal fixation system. Illustrative examples of screws include, butare not limited to, phillips screws, metric screws, standard screws,bone screws, headless screws, top loading screws, or those devicesdescribed in U.S. Pat. Nos. 6,540,748, 6,485,491, 6,280,442, 5,558,674,5,616,144, 5,531,746, and 5,470,333, the contents of the entirety ofeach of which are incorporated herein by this reference. Oneillustrative example embodiment of a screw useful in the presentinvention is a headless screw 20, which together with one illustrativeexample embodiment of a retaining nut 22, is depicted in FIGS. 4A, 4Band 4C, and may be used to attach system 10 to the lower surface of thespinous process of the C2 vertebrae. Though a headless screw 20 andretaining nut 22 are depicted in FIG. 4A, any other type of suitablescrew may used. Headless screw 20 includes an elongated shaft S,extending from a distal tip T, which may be configured for penetratingbone, to a retaining end R. Threads 24 are disposed around the shaft S,extending from near the distal tip T back along the shaft S allowing forsecure rotational placement of the headless screw 20 into bone, such asthe C1 and C2 vertebrae. It will be appreciated that the depictedthreads 24 are illustrative only and any spacing and size of threadsufficient to retain the headless screw 20 or any other kind of screw inplace, such as bone threads, may be used. Retention threads 26 arelocated on the shaft S near retaining end R, and are configured torotatably connect with threads 28 disposed on the internal channel 23 ofthe retaining nut 22. Retention threads 26 are typically smaller in sizeand more closely spaced than threads 24. However, it will be appreciatedthat the depicted retention threads 26 are illustrative only and anyspacing and size of thread sufficient to retain a fastener to theheadless screw 20 may be used. A non-threaded area of shaft S, which maybe the thickness of the threads 24 or 26, may be disposed between thetwo sets of threads.

Retaining end R includes structures allowing headless screw 20 to berotatably inserted into bone. As depicted in FIG. 4C, a socket 30 may beformed in retaining end R, into which a tool can be inserted to rotatethe headless screw 20 by interaction with the sides thereof. It will beappreciated that, although depicted in FIG. 4C as hexagonal, socket 30may have any desired shape that allows a tool to be inserted therein,examples include square, triangular, irregular, and radially patternedsockets for customized tools. It will also be appreciated thatnon-socket tool interconnection structures may be used, such as one ormore slots for a screwdriver tip disposed on the retaining end R orwithin a shallow recess disposed thereon.

As depicted, retaining nut 22 may have a rounded lower end 27 forinteracting with system 20, which may have a beveled edge on fastenerhole 18, and an upper end 29 configured for attachment to a connectiontool, such as a wrench. As depicted, upper end 29 is as hexagonal,although any desired shape that allows a tool to be removably attachedthereto may be used, examples include square, triangular, irregular, andradially patterned upper ends for interacting with customized tools.

Another illustrative example embodiment of a headless screw 20 and aretaining nut 22, are depicted in FIGS. 12 and 13. As depicted in FIG.12, headless screw 20 may comprise a retaining protrusion 25 thatprevents the further progress of occipital-cervical spinal fixationsystem 10 toward distal tip T. Although retaining protrusion 25 isdepicted as a shelf like protrusion, it will be apparent to one ofordinary skill in the art that any protrusion that prevents the furtherprogress of occipital-cervical spinal fixation system 10 toward distaltip T may be used. Examples of retaining protrusions 25 include, but arenot limited to, shelves, bumps, spikes, knobs, radial protrusions, etc.

Further depicted in FIG. 12 is another illustrative example of aretaining nut 22, in this case being a simple hexagonal shaped nutthreaded to rotatably interact with retention threads 26. Althoughspecific kinds of retention nuts are depicted in FIGS. 4A, 4B, 4C, 12,13, and 14, it will be apparent to one of ordinary skill in the art thatany shape or size of retaining nut 22 may be used. As will be furtherapparent to one of ordinary skill in the art, retaining nut 22, may notbe a nut at all, but may be any means for preventing theoccipital-cervical spinal fixation system 10 from slipping off ofretaining end R. Various forms of nuts depicted herein are understood tobe simply examples of means that may be employed for preventing theoccipital-cervical spinal fixation system 10 from slipping off ofretaining end R.

Depicted in FIG. 13 is one illustrative example of a horizontal crosssection of a headless screw 20. As depicted therein, a screw, such asheadless screw 20 may have a socket 30 as described above and/or ahollow shaft or cannula 32 disposed therein. Although cannula 32 isdepicted as running in a straight line from retaining end R to distaltip T, as will be apparent to one of ordinary skill in the art, thecannula 32, may run through the screw at any angle and may changedirections within the screw such that the openings of cannula 32 do notalign and/or may open into the side and/or ends of elongated shaft S,distal tip T, and/or retaining end R.

Depicted in FIGS. 14A, 14B, and 14C, is a further illustrative exampleof a retaining nut 22 according to the present invention. Depicted inFIG. 14A is a cross section of a retaining nut 22 having a drive socket31 disposed within upper end 29 and retention socket 35 disposed withinlower end 27. Disposed on the sides of retention socket 35, retainingthreads 28 are visible.

Depicted in FIG. 14B is an end on view of upper end 29 showing drivesocket 31. As will be apparent to one of ordinary skill in the art,although drive socket 31 is depicted as hexagonal in shape, drive socket31 may have any desired shape that allows a tool to be inserted therein,examples include square, triangular, irregular, and radially patternedsockets for customized tools. It will also be appreciated thatnon-socket tool interconnection structures may be used, such as one ormore slots for a screwdriver tip disposed on the upper end 29 or withina shallow recess disposed thereon.

Depicted in FIG. 14C is an end on view of lower end 27 showing retentionsocket 35 and retaining threads 28.

Fixation system 10 may be configured in dimension for installation in achild. Such configuring may account for both the smaller size of achild's head and neck, as compared to an adult, and for the differentallometric relationship of the head to the neck in a child. For example,in one illustrative embodiment, the length from the top of plate 12 tothe first set of bends 20A and 20B, depicted by line 100 (FIG. 3.) andincluding the plate and the upper section of legs 14A and 14B may bearound 32 mm. A second length between the two bends 20A and 20B and 30Aand 30B, as represented by line 102 (FIG. 3) may be around 22 mm. Athird length between the second bend 30A or 30B and the distal end ofthe respective legs 14A and 14B may be around 6 mm as depicted by line104. A ratio of 16:11:3 may thus be realized. It will be appreciatedthat different lengths may be used for each of these features, dependingon the age and anatomy of the patient. Accordingly, different ratios maybe used for children at different stages of development.

Table I below provides some illustrative examples of measurements (inmillimeters) that may be used on some embodiments in accordance with theprinciples of the present invention. Embodiment 1 2 3 4 5 6 7 8 Platethickness 3 3 3 3 3 3 3 3 Coronal Width 26 28 30 32 34 36 38 40 DistanceBend 18 20 22 24 26 28 30 34 A to Bend B Distance Bend 30.4 31.2 32 32.833.6 34.4 35.2 36 B to Coronal tip (generally variable be- tween 30 and36, dependent on patient need) Plate width 7 7 7 7 7 7 7 7 Accepts Screw3.5 3.5 3.5 3.5 3.5 4 4 4 SizeIn such embodiments, tab length may be between 6 and 10, plate thicknessmay be around 7 and arm width may be around 8.6. All measurements aregiven in mm and are merely illustrative. Embodiments have differentmeasurements are contemplated within the scope of the present invention.For example, larger embodiments of a system may be constructed for usein adult patients. For smaller adult patients or patients withanatomical variations, different embodiments may be constructed havingdifferent dimensions as appropriate for the patient.

The curve of legs 14 when extending from plate 12 may also be expressedas a ratio. As depicted in FIG. 3, the inside curve of the bend may havea radius of approximately 12.5 mm (as depicted by arrow 106), while theouter curve may have a radius of about 22 mm (as depicted by arrow 108),giving a ratio of 12.5:22. Each leg 14 may have a width of around 7.8 mmand be spaced apart from each other in a common plane by about 30 mmmeasured from a centerline axis of each leg 14. In such a sizedembodiment, the system may have a thickness of around 2 mm and the edgesof the system may be rounded to about 1 mm. Again, it will beappreciated that these measurements are for one merely illustrativepediatric embodiment and that embodiments having different measurementsare contemplated within the scope of the present invention. For example,larger embodiments of a system may be constructed for use in adultpatients, which could maintain a similar ratio for these curves.

Once being made aware of the system 10, those of ordinary skill in theart will be readily able to make the components thereof with the use ofconventional materials. For example, the plate 12 may be formed from anysuitable biocompatible material, including metal, such as titanium,stainless steel, cobalt-chromium-molybdenum alloys, titanium-aluminumvanadium alloys, other metals and alloys, or even a biocompatibleplastic, such as an ultra high molecular weight polyethylene. Arms 14Aand 14B may be constructed from similar suitable materials. It will alsobe appreciated that the means for attaching the fixation system to theC2 vertebra, such as, for example, headless screws 20, retaining nuts 22and the means of attaching the system to the occipital bone, such as,for example, attachment screws 160, may be constructed of similarmaterials.

FIGS. 5 through 9 show the installation and use of one embodiment of asystem 10. As best depicted in FIG. 9, upon the completion ofinstallation, the plate 12 is fastened to the occiput O with at leastone attachment bone screw 160 passing through one of the attachmentholes 16. Where desirable, multiple attachment bone screws 160 may beused in the different attachment holes 16. Where possible, it may bedesirable that at least one bone screw 160 be placed into the midlinekeel of the occiput O. Multiple attachment holes 16 may allow suchplacement with minimal adaptation of the system 10. A transarticularheadless screw 20 passes through fastener hole 18 in each arm 14 andinto both the C2 and C1 vertebrae, attaching the system 10 thereto inconjunction with the retention nut 22 rotatably retained thereon. Itwill be appreciated that a bone screw having a head, rather than aheadless screw 20 may be used in conjunction with system 10, as will beexplained further herein.

Typically, prior to installation, a detailed image of the patient'soccipital-cervical region is performed, such as a thin-cut CT scan orother appropriate imaging technique, to allow selection of anappropriate system 10 and guidance through the procedure. The placementof the system 10, and the attachment screws may be performed underintraoperative fluoroscopy. For placement, the system 10 may be placedin position, the attachment and fastener hole positions marked. Thesystem 10 may then be removed and the attachment sites prepared forinsertion of screws, which may involve placement or partial emplacementthereof. As depicted in FIG. 5, screws, such as headless screws 20 maybe placed transarticularly passing angularly upwards through the C2vertebra into the C1 vertebra (as depicted in FIG. 8) using anemplacement tool E. Where appropriate, paths for the insertion of thescrews may be drilled prior to insertion. Where headless screws 20 areused, the screws may then be left in place and the system 10 mountedwith the retention end R of each screw protruding through an attachmenthole 18A or 18B, as depicted in FIG. 6. Where headed screws are used,the screws may be entirely or partially emplaced, then removed, theplate positioned and the screws re-emplaced to attach the system 10. Insome embodiments, fastener hole 18 may have a keyhole 50 extension thatallows the system to be emplaced around a partially insertedtransarticular screw, as shown in FIG. 11A. Fastener hole 18 may also beformed as a recessed slot 52 (FIG. 11B) allowing for adjustment of thesystem during emplacement, following insertion of the screws.

Attachment is completed by the attachment of the plate 12 the occiput Owith at least one attachment bone screw 160 passing through one of theattachment holes 16. Multiple attachment bone screws 160 may be used inthe different attachment holes 16. Where possible, at least one bonescrew 160 may be placed into the midline keel K of the occiput O.Multiple attachment holes 16 may allow such placement with minimaladaptation of the system 10. Where appropriate, paths for the insertionof the bone screws may be drilled prior to insertion.

A bone graft material G, such as iliac crest or rib, (FIG. 9) may beplaced between the occiput O and the vertebrae to promote fusiontherebetween. The system 10 retains the bone graft material G in properposition and under compression to facilitate fusion between the occiputand the vertebrae, using a cable C, which is wrapped around the system10 to retain the bone graft B in place. From the foregoing discussion,it will be apparent that use of a system or method in accordance withthe present invention may lead to short surgery times and strongersystems than current procedures.

It will be appreciated that systems and methods of the present inventionmay be used to treat craniocervical junction instability through fusionof the occiput-C2 region, where the instability results from any cause,so long as patient's is sufficiently healthy to undergo implantationsurgery and the patient's anatomy will allow successful implantation.Examples of causes of such instability that may be treated with thesystems and methods of the present invention include trauma, osodontoideum, congenital anomaly (such as Down syndrome, Stihl disease,metatrophic dwarf, Morquio syndrome, Klippel-Feil syndrome, axisassimilation, or skeletal dysplasia), neoplasm, rheumatoid arthritis, orchronic instability.

FIG. 10 depicts a back view of another embodiment of a system 10A inaccordance with the teachings of the present invention. Similar tosystem 10, system 10A differs by having an enlarged plate 12A with anadditional attachment hole 16A, that extends down between the arms 14 ofthe system. Such a system 10A may facilitate placement attachment bonescrew 160.

FIGS. 11A and 11B depict alternative embodiments of fastener holes 18.For example, fastener hole 18 may have a keyhole 50 extension thatallows the system to be emplaced around a partially insertedtransarticular screw having a head, as shown in FIG. 11A. Fastener hole18 may also be formed as a recessed slot 52 (FIG. 11B) with a shelf 51therein allowing for adjustment of the system during emplacement,following insertion of the transarticular bone screws.

In order to facilitate use of a spinal fixation system in accordancewith the present invention, a kit is included within the scope of thepresent invention. Such a kit may include a system in accordance withthe present invention (such as a system 10 or 10A), means for attachingthe fixation system to the C2 vertebra, such as, for example,transarticular screws or headless bone screws 20, retaining nuts 22,means of attaching the system to the occipital bone, such as, forexample, attachment bone screws 160, drill guides, cable (such as atitanium cable), taps and calipers, all sized appropriately for usetogether. Such a kit may be provided in sterile form in a sealed sterilecontainer. Individual kits may be selected based on the size of thesystem 10 or 10A appropriate for the intended usage.

EXAMPLES

Data used in this example was also used in preparing the paper, Gluf andBrockmeyer, Atlantoaxial transarticular screw fixation: a review ofsurgical indications, fusion rate, complications, and lessons learned in67 pediatric patients, J. Neurosurg Spine 2:164-169, 2005, thedisclosure of which is incorporated herein by reference.

23 pediatric patients were treated for occipital cervical instability byoccipitocervical fusion performed with implants in conjunction withC1-C2 transarticular screws. While older patients were treated usingOhio Medical Instruments U-loop, rod/plate devices, patients from theages of 2 to 5 years of age were treated using a system in accordancewith the present invention, referred to as the Avery Brockmeyer-Thiokolplate, sized to fit patients 2 to 5 years of age.

A preoperative imaging protocol including plain cervicalflexion-extension radiography and thin-cut (1-mm) CT scanning of theocciput—C3 region with sagittal and coronal reconstructions wasperformed. However, no presurgical flexion-extension x-ray films wereobtained in traumatically injured patients with obviously unstableatlantoaxial or craniovertebral fractures. Craniovertebral magneticresonance imaging was found to be helpful in some cases but not criticalin the planning phase for placing C1-C2 transarticular screws. Imageanalysis of the thin-cut CT scan was performed on a high-speed CTworkstation with multiplanar reconstructions in the screw trajectorypathway being generated to determine the best path for screw placement.

In general, 3.5-mm-outer-diameter screws were used for transarticularplacement in patients 4 years of age and younger and 4-mm-outer-diameterscrews for patients older than the age of 4 years. However, as each caseis individualized, however, appropriate screw diameter for each patientwas determined only after careful study of the reformatted CT scans.

Before surgery, an understanding of the anatomical landmarks fordetermining the starting point for screw trajectory was obtained. Thescrew starting point is measured in millimeters from the midportion ofthe C2-C3 facet joint and the screw trajectory is defined in number ofdegrees from both the parasagittal plane and the dorsal or ventralposition of the screw relative to the VA foramen in C-2. Where apatient's anatomy was unsuitable for using C1-C2 transarticular screwson either side, a pars screw was placed, which was found to be usuallysufficient to anchor the chosen type of occipitocervical hardware.

Once the patient was intubated (either with axial traction or with ahard collar in place), he or she was lifted and turned carefully intothe prone position. Mayfield three-point fixation was routinely used inall patients, even those as young as 2 years of age. Gentle axialtraction was applied (except in cases of occipitoatlantal dislocation)under direct lateral fluoroscopic vision and the patient's neck flexedand posteriorly translated into the so-called military tuck position.During occipitocervical fusion, the patients were realigned into aneutral position prior to placing the rigid occipito cervicalinstrumentation to avoid the problem of fusion occurring in anonanatomical flexed position.

Postoperative imaging demonstrated successful fusion in all patients.Postoperative imaging included plain radiographs obtained at 1 and 2months and fine-cut CT scans of the occiput—C3 region reconstructed twodimensionally 4 months after surgery. If solid fusion was not evident onthe 4-month CT reconstruction, monthly repeated CT scanning involvingthe same protocol used in the 4-month study was performed untilconfirmation of fusion. Fusion was defined as continuous, bridgingtrabecular bone seen between the occiput and C-2 on two-dimensionalsagittal reconstructions of thin-cut CT scans indicated fusion.

It will be apparent that details of the apparatus, processes, andmethods herein described can be varied considerably without departingfrom the concept and scope of the invention.

1. A method of treating an occipito-cervical instability by performingan occipito-cervical fusion, the method comprising: positioning aone-piece occipital-cervical spinal fixation system in contact with theoccipital bone such that a plate configured for attachment to theoccipital bone is in contact therewith and arms extending outward fromthe plate pass behind the spinous process of the C1 and C2 vertebrae andcontact the C2 vertebra; marking an attachment site on the C2 vertebra;inserting at least one means of attaching the occipital-cervicalfixation system to the C2 vertebra into the C2 vertebra; attaching atleast one arm of the occipital-cervical fixation system to the C2vertebra with the at least one means of attaching the occipital-cervicalfixation system to the C2 vertebra.
 2. The method according to claim 1,wherein inserting at least one means of attaching the occipital-cervicalfixation system to the C2 vertebra into the C2 vertebra comprisesinserting at least one screw into the C2 vertebra.
 3. The methodaccording to claim 2, wherein inserting at least one screw into the C2vertebra comprises inserting a headless screw comprising an interconnectstructure on a proximal end thereof into the C2 vertebra.
 4. The methodaccording to claim 3, wherein inserting a headless screw having aninterconnect structure on a proximal end thereof into the C2 vertebracomprises inserting a headless screw comprising retaining threads on aproximal end thereof into the C2 vertebra.
 5. The method according toclaim 4, attaching at least one arm of the occipital-cervical fixationsystem to the C2 vertebra with the at least one means of attaching theoccipital-cervical fixation system to the C2 vertebra comprisesattaching a retaining nut to the retaining threads to secure the atleast one arm to the C2 vertebra.
 6. The method according to claim 2,wherein attaching at least one arm of the occipital-cervical fixationsystem to the C2 vertebra with the at least one means of attaching theoccipital-cervical fixation system to the C2 vertebra comprisesretracting the at least one screw from the C2 vertebra, placing thesystem in place and reinserting the at least one screw into the C2vertebra through an attachment hole in the at least one arm.
 7. Themethod according to claim 2, inserting at least one screw into the C2vertebra comprises inserting at least one cannulated screw into the C2vertebra.
 8. The method according to claim 2, inserting at least onescrew into the C2 vertebra comprises inserting at least oneself-drilling screw into the C2 vertebra.
 9. An occipital-cervicalspinal fixation system, comprising: a plate; a first arm extending froma first side of the plate and curving to extend at a ninety degree anglefrom the plate; a second arm extending from a second side of the plateand curving to extend at a ninety degree angle from the plate, thesecond arm running in a common plane with the first arm along its entirelength and parallel thereto at a point distal to its curving; a firstextension bend in the first arm, such that the first arm will extendoutward from the occipital bone upon attachment of the plate thereto,passing behind the spinous process of the C1 and C2 vertebrae; a secondextension bend in the second arm in-line with the first extension bend,such that the second arm will extend outward from the occipital boneupon attachment of the plate thereto, passing behind the spinous processof the C1 and C2 vertebrae; a first connection bend in the first arm,such that the first arm will contact the C2 vertebrae upon installationof the plate to the occipital bone; a second connection bend in thesecond arm, such that the second arm will contact the C2 vertebrae uponinstallation of the plate to the occipital bone; a first attachment holein the first arm near a distal end thereof; a second attachment hole inthe second arm near a distal end thereof; and at least one means ofattaching the occipital-cervical fixation system to the C2 vertebra. 10.The system of claim 9, wherein at least one means of attaching theoccipital-cervical fixation system to the C2 vertebra comprises a screw.11. The system of claim 10, wherein the screw comprises an interconnectstructure on a proximal end thereof.
 12. The system of claim 10, whereinthe screw comprises retaining threads on a proximal end thereof.
 13. Thesystem of claim 10, wherein the screw is a bone screw.
 14. The system ofclaim 10, wherein the screw is a headless screw.
 15. The system of claim10, wherein the screw is cannulated.
 16. The system of claim 10, whereinthe screw is a top loading screw.
 17. The system of claim 10, furthercomprising at least one retaining nut.
 18. The system of claim 10,wherein the screw comprises a retaining protrusion.
 19. A kit forperforming an occipital-cervical fusion, the kit comprising: an implantfor performing an occipital-cervical fusion, said implant having anenlarged top portion with at least one connection hole therethrough forconnection to the occipital bone, a first arm and second arm extendingopposite from one another then turning downwards to parallel each other,each arm having an attachment hole near the distal end, and each armhaving a first bend and a second bend along its length, such that theeach arm will extend outward from the occipital bone passing behind thespinous process of the C1 and C2 vertebrae and contact the C2 vertebraeupon installation; at least one means of attaching at least one of thefirst arm or second arm to the C2 vertebra to the C2 vertebra; and atleast one means for attaching the implant to the occipital bone.
 20. Thekit of claim 19, wherein the at least one means of attaching at leastone of the first arm or second arm to the C2 vertebra to the C2 vertebraand/or the at least one means for attaching the implant to the occipitalbone comprise a screw.